The coefficient of xkin the expansion of 1−2x−x2ex is

manpreet Best Answer 3 years ago

The coefficient of xkxkin the expansion of 1−2x−x2ex1−2x−x2ex is

This a question of university entrance examination, which my teachers didn't taught me and not in my syllabus.

I referred got this equation from Hall and Knight Algebra :

Coefficient of xrxr in the expansion of 1−ax−x2ex1−ax−x2ex is given by

−1rr!{1+ar−r(r−1)}−1rr!{1+ar−r(r−1)}

 

However applying this answer gives me :